What is an included crystal?

An included crystal refers to a mineral crystal that is trapped within a gem during its growth. This phenomenon occurs when the gemstone forms, and an external mineral is inadvertently incorporated into the structure of the gem. Such inclusions are significant because they can affect the gem’s appearance, clarity, and overall value.

In the context of the choices, this definition aligns directly with the nature of inclusions in gemstones. Inclusions are often studied by gemologists to gain insights into a gemstone's origin and history, as well as to assess its quality.

Understanding the presence of included crystals is essential for evaluating gemstones as these inclusions can contribute to the uniqueness of the stone, influencing its character and appeal. In contrast, the other choices pertain to various unrelated aspects of crystals and gemstones, such as enhancement techniques, visible inclusions for grading purposes, or specific geological contexts for crystal formation, which do not accurately capture the definition of an included crystal.